SPARK3D User Manual
Multipactor practical considerations

Secondary Emission Yield (SEY)

The multipactor discharge is a complex physical phenomenon which is strongly related to many factors. Concretely, the most important one is the Secondary Emission Yield (SEY) of the surfaces of the device.

The correct modeling of the SEY properties of the surface is crucial for having reliable simulations. SPARK3D multipactor module, allows for using custom SEY parameters or even importing ASCII SEY definition files (see material definition).

Unfortunately, in the real world, there is a high uncertainty with the real values of the SEY:

See below an example in Table 1, where the measured SEY properties of silver coatings coming from different companies are compared (extracted from [1], company names are confidential). A big difference can be observed. Values measured at different moments are also presented, showing a noticeable variation.

 

Table 1: Comparison of Silver SEY for different companies and variation with time (Ageing).

 

Initial

After 6 months

After 18 months

 

E1

SEYmax

Emax

E1

SEYmax

Emax

E1

SEYmax

Emax

Company1

20

2.8

380

20

3.1

298

20

3.1

268

Company2a

40

1,9

410

29

2,1

322

24

2,6

288

Company2b

44

2,0

484

39

2,3

376

39

2,2

376

Company3

43

1,7

210

34

2,1

366

34

2,1

385

 

With all this in mind, the engineer must interpret the breakdown discharges given by the software with caution, expecting some margin in experimental measurements. Our recommendation is to do a SEY sensitivity analysis, simulating the same structure with different SEY curves, to see the impact on the breakdown power, since this impact will strongly depend on the particular component under analysis.

 

Standard SEY materials

SPARK3D includes typical SEY parameters for most relevant materials, extracted from European ECSS standard [2] and The American Aerospace Corporation standard [3]. Both standards give worst-case multipactor breakdown charts which may be useful to easily estimate the breakdown levels for the parallel-plate case. For real structures, numerical simulation with SPARK3D provides more accurate results.

The ECSS standard figures correspond to different materials and come from the fitting of the multipactor breakdown results to a particular test campaign done in [4]. For that reason, numerical simulations with SPARK3D (with simple structures, close to parallel-plate geometry) and ECSS SEY parameters,  provide results similar to those of the ECSS standard.

In turn, the SEY parameters provided by The Aerospace Corporation standard do not correspond to real measurements, but correspond rather to a single material which represents theoretically the worst-case (lowest breakdown levels). On the other hand, The Aerospace Corp. standard is based on the classical multipactor theory for parallel plates without experimental data fitting. As a result, numerical simulations with SPARK3D (with simple structures, close to parallel-plate geometry) and The Aerospace Corp. SEY,  provide more realistic (higher) breakdown levels. Figure below shows the difference (around 3 dB).

 

References

[1] ESA-ESTEC TRP AO/1-4978/05/NL/GLC "SEY Database",  Final Report, December 2011.

[2] "Space Engineering: Multipacting Design and Test", volume ECSS-20-01A, edited by ESA-ESTEC. ESA Publication Division, The Netherlands, May 2003.

[3] AEROSPACE REPORT NO. TOR-2014-02198, "Standard/Handbook for Radio Frequency (RF) Breakdown Prevention in Spacecraft Components"

[4] A. Woode and J.Petit. "Diagnostic investigations into the multipactor effect, susceptibility zone measurements and parameters affecting a discharge". Technical report, ESTEC working paper No. 1556, Noordwijk, Nov. 1989.

 

Limitations

Presently, all surfaces in the problem are considered to have the same SEY properties. This is, regarding to Secondary Emission Properties, there is no distinction between different metals or dielectrics within the same problem. They all will be assigned a common SEY curve defined by the user.

Due to numerical limitations on the electron path integration, in rare cases and for very high fields, false single-surface discharges may occur at very low multipactor orders (below 0.05). These are easily identified and must not be taken as real discharges. If this occurs, please contact technical support for possible solutions to this issue.

Errors

Due to the nature of the phenomenon, the results can slightly differ from simulation to simulation. This deviation can be considered an intrinsic error caused by the phenomenon itself. However, this error is normally so small that it is not relevant for practical applications.